Conventionally, touch sensor-equipped display devices provided with a touch sensor (also referred to as a touch panel) on the front surface (viewer side) of a display have been used in various applications. A touch sensor is an input device that makes possible operation commands or data input by detecting the position where a finger, a stylus, or the like has come into contact. In terms of the types of position detection, the capacitance coupling type, the resistive film type, the infrared type, the ultrasonic type, the electromagnetic inductive/coupling type, and the like are known.
When using a touch sensor integrally with a display device, there is a problem that the touch sensor receives noise from the display device resulting in a decrease in the accuracy of position detection. In a case in which the display device uses a liquid crystal panel, for example, common voltage applied to an opposite electrode of the liquid crystal panel causes an induced voltage to occur in the conductive film for position detection of the touch sensor. This induced voltage is a cause for noise.
A configuration for eliminating such noise is disclosed in Japanese Patent Application Laid-Open Publication No. 2006-146895, for example. A touch sensor-equipped display device disclosed in the aforementioned publication is provided with a strobe signal generation circuit and a noise reduction current signal generation circuit. The strobe signal generation circuit generates a strobe signal in synchronization with the period of polarity reversal of the common voltage supplied to the opposite electrode. The noise reduction current signal generation circuit generates a noise reduction current signal, which is obtained by eliminating, based on the strobe signal, prescribed portions from a current flowing from terminals connected to the touch sensor part.
According to this conventional configuration, the noise occurring in an output current of the conductive film for position detection caused by a periodic polarity reversal of the common voltage is eliminated using the strobe signal. As a result, the S/N ratio of the touch sensor output is improved and the accuracy of the position detection is improved.
However, with the above-mentioned conventional configuration, specialized circuits for noise-removal such as the strobe signal generation circuit and the noise reduction current signal generation circuit are needed, resulting in a complex configuration.